Electromagnetic pick-up



Ma3 '6,1930. MALDEN l 1,756,966

ELECTROMAGNETIC PICK-UP Filed Jan. 17, 1927 INVENT R Ratented May 6,1930

: UNITED STATES PATENT OFFICE mirror ALDEN, or srnmermnn, massacnusm'rs,ASSIGNOR To run ALDEN an'urac'runme comrnmr, or naocxroiv,massacnusnrcrs, A coaromrron or massacnusnrrs Application filed January17 1 The main ob ect of my invention 1s to produce a devlce' orthe'conversion of the me- 'chanical movement of a needle or styluscaused by the undulations ofthe grooves ofa 5 sound record intoelectrical pulsations of corresponding frequency and ainplitude'-suchdevises are frequently called magnetic pickups.

" Another object is to provide a device of the above descri tion inwhich the moving parts are light an therefore of little inertia andhence readily able to accurately follow the above describedhaving ashort air-gap, hence undulations of the-record.

Another object isto producea device .as

a large percentage change of magnetic cirtivity.

cuit reluctance and thereforeof high sensi- Another object is to producea magnetic pick-up which will operate on-the typeof record whichproduces movement in a plane view of still another embodiment.

. 1 In Fig. 1 thepole pieces 5 and 6 are secured in some convenient,manner to the ends of the'permanent magnet 7 On-these pole transversetothe axis of the stylus or on a record which produces movement alongsaid axis b merely'motating the reproducer into i pieces are mounted thebobbins or spools 8 and 9 which carry the windings 10 and 11,, which maybe connected to the input of a .suitable' am lifier (not shown).The-arma-.

'ture12 is he d against the pole tip 13-,by means Oftllfl resilientwasher 14 which is pressed uponby-the bar or strip 15. .This strip 15,

is provided with an aperture 16 of sufficient w si'z'eto afford adequateclearance for the stylus-holder 17., The stylus holder 17 is secured tothe armature 12 at a point such as,

f18 close to the-point of contact with the pole tip 13. The po'sitionofthe bar 15 is regu- 'Iated by thethumb screws 19and 20 whlch operate inthe threaded bushings studs'21 and ner.

nnncrnomaeimric PICK-UP 1927. a Serial m. 161,620.

22. It will be seen that adi'ustment of the nut 20 will PI'OdIiICG alarge 0 iange inthe air gap 23 between t e armature 1 2 and the pole gapcan be left unc anged and the compres sion of the resilient washer 14may be varied, thus afi'ectin the damping of the armature or reed .12.%t will be seen that the lateral motion of the stylus 25 will change theair gap 23, thus changing the magnetic circuit consisting of thepermanent magnet7, the

pole iece 6, the armature 12, the air gap 23 and t e pole piece 5', thusproducing voltages, substantially proportionate to this movement,

in the wlndings 10' and 11 which ma be amplified and reproducedin anysuita le man- With :the more usual type of lateral cut record in whichthe music is recorded by radial changes of the needle path along therecord, the section shown in Fig. 1 would be along the plane passingthrough the radii of the record, but if the reproducer is rotatedthrough90 degrees so that the section shown is in a plane normal to a radii ofthe record, the hill and dale type of record will produce the desiredmovement of the armature.-

tip 24, while by ad'usting both nuts the air 4 .In Fig. 2 the armature12 is secured in any suitable mannerdirectly to the pole piece 13 as bythe screw 13. Two resilient damping bloc s and 31 are .placed on eitherside of the armature and are held between the annature and the spoolhead 32 and between the armature and the clamping bar 33, respectively.The knurled nut 34 is then used to regulate the size of the air gap'2 3.The mag-' netic system of the embodiment shown in Fig.

2 is similar to that of Fig. 1 and Fig. 3.

'In-Fig. 3 the stylus holder 17 carries a collar 40 which is] preferabmade integral. This collar is supported In two yielding or. resilientwashers .41 and-42. The washer 41 is'positioned on the adjusting bar 43by the externally threaded ring whose interior threads engage thethreads of the ring 44 serves to clamp the. washer 42 against the collar49 of the stylus 17 The on is provided with an' aperture'46 of Sn cientsize to allow adequate freedom of movement of the stylus holder 17 Byrotat- 44. The cup 45 I ing the cup 45 the clamping action of the tworesilient washers 41 and 42 upon the col-- lar may be varied, thusvarying thedamping' action upon themoving parts. The relative clearancebetween the pole pieces 13 and 24: and. the armature 12 may also beregulated by the rotation of the knurledsheaded screws 47 and48.

In all three embodiments shown the stylus 25 is secured in .the stylusholder 17 by the thumb screw 49.

It has been foundthat the structures destgibed are highlyeflicientneeding less amp fication for a given outputvolume than isusuallyconsidered necessary. By using but one air gap and having thatadjustable so that it can be made smaller than would be manufacturablvpracticable if made fixed, a large change of magnetic reluctance withextremely small movement is secured, which I believe accounts forthehigh sensitivity.

The simplicity and lightness of the moving parts, combined with the factthat these parts are yieldingly held in position, produces, extremelyfaithful reproduction and the natural period and harmonics of thearmature do not cause the I corresponding frequencies to, be emphasizedas often occurs ii other devices of this nature. I

It is also possible by varying both the air gap and the yieldinglycompressive force, which holds the armature in position, to

change the characteristic of. the device sufliv armature near its thetwo spoles.

ciently to make it adjustable for a wide range of amplifiers, or othervarying conditions.

It is not unusual in devices of this nature for the air gap to becomeclogged with fillings, dust or. other foreign material. With myconstruction the armature may be readily re- .moved and such materialwiped from the armature and pole-tip. It is also extremely easy toreplace the armature and stylus hold- .er in case it becomes bent,crystallized or otherwise injured.

Another novelfeature of my device is that the adjustment of the air. gapand damping may be. effected by means of the screws such .as 19,,20, 47and 48 while a record is being played and can thus be adjusted withlittle difiiculty to maximum sensitivity or to suit the personalquality.

I claim:

1. A double pole magnet havin an armature pivotally supported by one 0said poles normally out of engagement with the-other pole and a stylusdirectly attached to the pivoted end andbetween preferences of theuseras to 2. In a magnetic pick-up a bi-polarmagnetic system and having anarmature in contact with one pole, a stylus carried by said armature, adamping member adjacent to said stylus, and common means for adjusting.the

damping member and the air gap, said means acting directly on saiddamping member.

3. A magnetic pick-up device comprising a magnet having pole piecesprojecting from one side, an armature pivoted below one pole piece, astylus carried by the armature, a

damping means 'for said armature, and a screw having an ad ustmg endvaccessible supported by one of said poles normally out v of engagementwith the other pole, one ofsaid pole pieces, said armature having astylus holder rigidly attached .to said armature at apoint on saidarmature between-"said pole pieces and at right angles to said armature.

5. A magnetic pick up having a magnetii: system consisting of apermanent magnet having two pole-pieces carrying windings, an armaturepivotally supported by one of said poles normally out of engagement withthe other pole,-and a stylus directly attached toand disposed at rightangles to said armature and between said p'ole pieces so as to vary thereluctance of said magnetic system substantially in accordance with thevariations of, a sound record, said armature be-= ing yieldinglysupported against said con-,-

'tacting pole-piece.

6. A magnetic pick-up having a magnetic system consisting of a permanentmagnet havarmature pivotally supported by one of said poles normally outof engagement with the other pole, and a stylus directly attached towith the type of sound record whose'varia-g tions are radial or with thetype of sound record whose variations are parallel to its axis ofrotation. v

MILTON ALDEN.

ing two pole pieces carrying windings, an

' and disposed at right angles to said armature

